A SINGLE-MOUSE GENE ENCODES THE MITOCHONDRIAL TRANSCRIPTION FACTOR-A AND A TESTIS-SPECIFIC NUCLEAR HMG-BOX PROTEIN

Mitochondrial transcription factor A (mtTFA) is a key regulator of mam malian mitochondrial DNA transcription. We report here that a testis-s pecific isoform of mouse mtTFA lacks the mitochondrial targeting seque nce and is present in the nucleus of spermatocytes and elongating sper matids, thus representing the first reported mammalian gene encoding p rotein isoforms targeted for the mitochondria or the nucleus. The pres ence of the mitochondrial transcriptional activator in the nucleus rai ses the possibility of a role for this protein in both genetic systems . Mutations in the nuclear mtTFA gene may therefore exhibit phenotypic consequences due to altered function in either or both genetic compar tments.